Heavy duty internal combustion engines and more specifically diesel engines, have accounted for a high percentage of the prime power for heavy duty on-highway truck applications. Over the many years these engines have been utilized, there have been continuing efforts to enhance durability, reliability and performance. One of the principle performance criteria by which an engine is judged is normal oil consumption. In early years it was not uncommon to have oil consumption as low as 1 quart for every 100 miles. Because of current efforts oil consumption has been greatly improved. One of the ways in which oil consumption has attempted to be improved is by recognizing the role of top compression ring reversal in unseating at or near top dead center. The typical modern day piston has a plurality of compression rings on an annular piston with an oil control ring at the bottom. The top compression ring is the first barrier to gas pressures passing down the side wall of the piston. As the engine is displaced toward a top dead center or a minimum volume, the pressure in the cylinder keeps the top compression ring seated against the lower wall of its ring groove. When combustion takes place, the pressure on the piston also tends to force the ring against its lower seat. However, when by-pass gases from the combustion process leak through the end gap or other clearances at the top ring, a dynamic and momentary pressure is created in-between the top ring and the second from the top ring. This temporary increase of pressure exists at a time when the combustion pressures are decaying as the piston is displaced towards bottom dead center. Frequently this pressure can rise to a point where it is greater than the pressure in the combustion chamber. As a result the top ring is unseated from the lower wall of its ring groove, thus permitting oil to pass into the combustion chamber. The consequence of this is an increase in oil consumption.
There have been a number of approaches to achieve a greater than normal volume between the top two compression rings so that the volume acts as an accumulator to delay the buildup of pressure and thus prevent the pressure from exceeding that of the combustion gases to cause unseating of the top ring. Such examples are found in U.S. Pat. Nos. 4,253,435 and 4,282,837. While these approaches take a step towards preventing top ring reversal. It is not possible for them to achieve a sufficiently great capacitance volume between the two rings in order to properly delay the buildup of pressure on the lower side of the top compression ring.